Not the expected alpha-shape

[stla]

Hello,

This is my pointcloud:

With a R package, I get the following alpha-shape for alpha = 0.1:

It is torus-like. This is the shape I'm expecting.

However with CGAL I get this one, without hole:

I tried numerous values of alpha, and never got the hole. Is it normal? I'm using Fixed_alpha_shape.

[stla]

I get it with the Delaunay triangulation! Above I used the weighted alpha-shape. Nice !